1. Field of the Invention
This invention relates to the recovery of, and purification of, compressible refrigerant contained in a refrigeration system. More specifically it relates to a method and apparatus for recovering an extremely high percentage of the refrigerant contained in a given system.
2. Description of The Prior Art
A wide variety of mechanical refrigeration systems are currently in use in a wide variety of applications. These applications include domestic refrigeration, commercial refrigeration, air conditioning, dehumidifying, food freezing, cooling and manufacturing processes, and numerous other applications. The vast majority of mechanical refrigeration systems operate according to similar, well known principals, employing a closed-loop fluid circuit through which a refrigerant flows. A number of saturated fluorocarbon compounds and azeotropes are commonly used as refrigerants in refrigeration systems. Representative of these refrigerants are R-12, R-22, R-500 and R-502.
Those familiar with mechanical refrigeration systems will recognize that such systems periodically require service. Such service may include removal, of, and replacement or repair of, a component of the system. Further during normal system operation the refrigerant can become contaminated by foreign matter within the refrigeration circuit, or by excess moisture in the system. The presence of excess moisture can cause ice formation in the expansion valves and capillary tubes, corrosion of metal, copper plating and chemical damage to insulation in hermetic compressors. Acid can be present due to motor burn out which causes overheating of the refrigerant. Such burn outs can be temporary or localized in nature as in the case of a friction producing chip which produces a local hot spot which overheats the refrigerant. The main acid of concern is HCL but other acids and contaminants can be produced as the decomposition products of oil, insulation, varnish, gaskets and adhesives. Such contamination may lead to component failure or it may be desirable to change the refrigerant to improve the operating efficiency of the system.
When servicing a refrigeration system it has been the practice for the refrigerant to be vented into the atmosphere, before the apparatus is serviced and repaired. The circuit is then evacuated by a vacuum pump, which vents additional refrigerant to the atmosphere, and recharged with new refrigerant. This procedure has now become unacceptable for environmental reasons, specifically, it is believed that the release of such fluorocarbons depletes the concentration of ozone in the atmosphere. This depletion of the ozone layer is believed to adversely impact the environment and human health. Further, the cost of refrigerant is now becoming an important factor with respect to service cost, and such a waste of refrigerant, which could be recovered, purified and reused, is no longer acceptable.
To avoid release of fluorocarbons into the atmosphere, devices have been provided that are designed to recover the refrigerant from refrigeration systems. The devices often include means for processing the refrigerants so recovered so that the refrigerant may be reused. Representative examples of such devices are shown in the following United States Patents: U.S. Pat. No. 4,441,330 "Refrigerant Recovery And Recharging System" to Lower et al; U.S. Pat. No. 4,476,688 "Refrigerant Recovery And Purification System" to Goddard; U.S. Pat. No. 4,766,733 "Refrigerant Reclamation And Charging Unit" to Scuderi; U.S. Pat. No. 4,809,520 "Refrigerant Recovery And Purification System" to Manz et al; U.S. Pat. No. 4,862,699 "Method And Apparatus For Recovering, Purifying and Separating Refrigerant From Its Lubricant" to Lounis; U.S. Pat. No. 4,903,499 "Refrigerant Recovery System" to Merritt; and U.S. Pat. No. 4,942,741 "Refrigerant Recovery Device" to Hancock et al.
When most such systems are operating, a recovery compressor is used to withdraw the refrigerant from the unit being serviced. As the pressure in the unit being serviced is drawn down, the pressure differential across the recovery compressor increases because the pressure on the suction side of the compressor becomes increasingly lower while the pressure on the discharge side of the compressor stays constant. High compressor pressure differentials can be destructive to compressor internal components because of the unacceptably high internal compressor temperatures which accompany them and the increased stresses on compressor bearing surfaces. Limitations on the pressure differentials or pressure ratio across the recovery compressors are thus necessary, such limitations, in turn can limit the percentage of the total charge of refrigerant contained within the unit being serviced that may be successfully recovered.
A refrigerant recovery system has been developed that operates in alternating modes of operation, a first recovery mode, recovers refrigerant through use of a recovery compressor which withdraws refrigerant and delivers it to a storage container. A second cooling mode, lowers the temperature and pressure of the recovered refrigerant in the storage container to thereby facilitate recovery of additional refrigerant in a subsequent recovery cycle. At the onset of the cooling mode of operation, under some conditions, the initially high temperature of the storage container may result in an unacceptably high compressor discharge pressure.